The invention relates to an injector device for a microwave filter unit that uses dielectric resonators, in particular a filter unit that includes channel filters whose outputs are combined by a common waveguide or manifold to multiplex them. It also relates to filter units, for example the kind of filter unit referred to above, that incorporate injector devices according to the invention.
Filter units of the kind referred to above are used in particular in the field of radio telecommunication systems and especially in equipment that is to be installed onboard satellites. This is known in the art.
One prior art solution for injecting energy into a multipole microwave filter unit is shown diagrammatically in FIG. 1, which represents an output multiplexer unit (OMUX). The output multiplexer unit includes two input channel filters with multiplexed outputs. Each channel filter includes two resonant cavities 1A, 1B or 1xe2x80x2A, 1xe2x80x2B whose modes are coupled by coupling irises. The cavity walls are made of conductive materials and are generally cylindrical or rectangular in shape.
Each channel filter receives a signal transmitted to it by a coaxial cable, for example the cable 2. The cable is connected to an input connector 3 or 3xe2x80x2 which injects the transmitted signal into a first cavity of the channel filter including the connector, for example the cavity 1A.
The signal received by a channel filter is filtered in the two cavities of the channel filter, which are equipped with appropriate resonator elements, not shown, as explained later. The signal filtered by a channel filter is transmitted from the second cavity of the channel filter, for example the cavity 5B, to a common waveguide 5 which constitutes the output element of the filter unit, in which the output signals of the channel filters are multiplexed. The second cavity of each channel filter is connected to the waveguide 5 by an output waveguide element; for example, the cavities 1B, 1Bxe2x80x2 are connected by the elements 6, 6xe2x80x2. Here the guide element is assumed to be disposed axially along the longitudinal axis of the row of cavities of the channel filter, for example the axis XXxe2x80x2 in the case of the channel filter 1. The positions of the output waveguide elements 6, 6xe2x80x2 and the input connectors 3, 3xe2x80x2 of a filter unit of the above kind of depend on the number of poles. This is known in the art.
In the four-pole filter unit shown the cavities are dual mode cavities and incorporate flat dielectric resonator elements perpendicular to a longitudinal axis common to the cavities of the channel filter accommodating them. The input connector of a channel filter is disposed as shown. This is not very satisfactory because it requires a relatively large space L between the channel filters to enable a coaxial cable to be connected to an input connector if the latter is between the respective two channel filters, like the coaxial cable connected to the connector 3 between the channel filters 1 and 1xe2x80x2.
In some cases it is preferable to use a six-pole filter unit to exploit the fact that the injection axes in the channel filters of the unit are then perpendicular to those of the connectors shown in FIG. 1, i.e. perpendicular to the plane of the figure rather than in it, as shown in the case of a four-pole filter unit. It is then possible to leave a much smaller space between the channel filters. However, even though they have the overall size drawback referred to above, filter units with four or five poles constitute a better response to the current specifications than six-pole filter units, which has led to attempts to produce an injector device that is not directly dependent on the number of poles.
European Patent Application EP-A-6961338 describes the bandpass filter unit shown in FIG. 2, which uses dielectric resonators and has input and output connectors 7 for coaxial cables disposed axially along the longitudinal axis YYxe2x80x2 of the row of cavities of the filter unit. The rectangular parallelepiped-shaped cavities are formed inside a metal housing 8 and each contains a dielectric resonator in the form of a thick disk, for example the resonator 9. Each disk is in a cavity and parallel to the bottom of the housing, and two adjacent cavities communicate with each other via a window formed in the wall between them, for example the window 10 in the wall 11. Microwave signals are injected and extracted through the two connectors 7, each of which is mounted in a respective one of the two walls that close the ends of the filter unit; each connector either injects a signal into a cavity of the filter unit at which it terminates or extracts a signal therefrom. Injection is effected through a magnetic coupling loop 12 connecting the conductive core of the injection coaxial connector to the ground to which the housing is itself connected. The use of this kind of magnetic coupling loop is disadvantageous in an industrial context because it is difficult to manufacture and is not readily reproducible in the context of mass production. Also, it applies only to filter units with monomode cavities.
The invention therefore proposes a channel filter injector device for a microwave filter unit using dielectric resonators including a plurality of channel filters with communicating dual mode cavities. Each channel filter includes a filter input cavity receiving a signal to be processed that is transmitted by a coaxial cable via a connector mounted through a wall closing said cavity at an entry end of the filter.
According to one feature of the invention, the injector device provided for a channel filter acts electrically on a resonator dielectric element housed in the input cavity via a probe consisting of a L-shaped rod having a first portion connected to the core of the coaxial cable to extend it into the cavity and a second portion which acts on said resonator dielectric element via electrical coupling means.
In one embodiment of the invention the probe acts on a flat resonator dielectric element perpendicular to a central axis of the input cavity accommodating it, said axis coinciding with the longitudinal axis of the channel filter of which said input cavity is part. The L-shaped rod of the probe has a first portion perpendicular to the plane that said resonator dielectric element defines and by which said element can be electrically excited and a second portion parallel to the plane defined by said resonator dielectric element and in the vicinity of said element in the input cavity accommodating them.
In a preferred embodiment of the invention the second part of a probe is disposed radially relative to the central axis of the input cavity accommodating it, in a direction that corresponds to that in which the resonator dielectric element close to it in said input cavity and on which it acts can be electrically excited.
The invention also proposes a microwave filter unit of the kind defined hereinabove including an injector device of the kind defined hereinabove for each channel filter.
According to the invention the filter unit can include at least one injector device having a probe whose second portion is disposed along a diagonal of a nearby flat resonator dielectric element which is at least approximately in the shape of a parallelogram whose corners are short-circuited together, at least at microwave frequencies, by the conductive wall of the input cavity accommodating said probe and said resonator element.